This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cardiovascular disease is a major health problem that is largely preventable through lifestyle modifications, such as increasing physical activity. Despite our clear understanding of the risks associated with a sedentary lifestyle, most Americans do not meet the recommended physical activity guidelines for maintaining cardiovascular health. Endothelial dysfunction is recognized as an early occurrence in the development of atherosclerosis, and its presence and severity are highly correlated with future cardiac morbidity and mortality. Failure of the vascular endothelium to produce the vasodilator NO in response to normal stimuli results in the impaired regulation of vascular tone and inflammation. Exercise training has been demonstrated to have beneficial effects on endothelial function in studies of both healthy individuals and those with an elevated risk or clinically diagnosed cardiovascular disease. The purpose of the current study is to determine the effect of exercise intensity on the acute changes in FMD in both lean and abdominally obese individuals. This study will be the first to examine the acute time course FMD measurements following a single bout of exercise. We hypothesize that the augmentation of FMD will be of greater magnitude and duration following 30 minutes of high-intensity compared with moderate-intensity exercise, and that this acute exercise effect will be observed in both healthy weight and obese adults (but may be attenuated in the obese). As a secondary aim, the timing of microvascular and macrovascular changes in the lower limb immediately following high-intensity exercise will be examined using Doppler ultrasound and contrast enhancement with Definity microbubbles. The results will contribute to our understanding of the factors involved in the effects of exercise on endothelial function, and systemic and microvascular blood flow, and may lead to more specific exercise prescription for those at risk for CVD.